/* hmac.c - TinyCrypt implementation of the HMAC algorithm */

/*
 *  Copyright (C) 2017 by Intel Corporation, All Rights Reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions are met:
 *
 *    - Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *
 *    - Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 *    - Neither the name of Intel Corporation nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 *  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 *  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 *  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 *  POSSIBILITY OF SUCH DAMAGE.
 */

#include <tinycrypt/hmac.h>
#include <tinycrypt/constants.h>
#include <tinycrypt/utils.h>

static void rekey(uint8_t *key, const uint8_t *new_key, unsigned int key_size)
{
    const uint8_t inner_pad = (uint8_t) 0x36;
    const uint8_t outer_pad = (uint8_t) 0x5c;
    unsigned int i;

    for (i = 0; i < key_size; ++i) {
        key[i] = inner_pad ^ new_key[i];
        key[i + TC_SHA256_BLOCK_SIZE] = outer_pad ^ new_key[i];
    }

    for (; i < TC_SHA256_BLOCK_SIZE; ++i) {
        key[i] = inner_pad;
        key[i + TC_SHA256_BLOCK_SIZE] = outer_pad;
    }
}

int tc_hmac_set_key(TCHmacState_t ctx, const uint8_t *key,
                    unsigned int key_size)
{
    /* input sanity check: */
    if (ctx == (TCHmacState_t) 0 ||
            key == (const uint8_t *) 0 ||
            key_size == 0) {
        return TC_CRYPTO_FAIL;
    }

    const uint8_t dummy_key[key_size];
    struct tc_hmac_state_struct dummy_state;

    if (key_size <= TC_SHA256_BLOCK_SIZE) {
        /*
         * The next three lines consist of dummy calls just to avoid
         * certain timing attacks. Without these dummy calls,
         * adversaries would be able to learn whether the key_size is
         * greater than TC_SHA256_BLOCK_SIZE by measuring the time
         * consumed in this process.
         */
        (void)tc_sha256_init(&dummy_state.hash_state);
        (void)tc_sha256_update(&dummy_state.hash_state,
                               dummy_key,
                               key_size);
        (void)tc_sha256_final(&dummy_state.key[TC_SHA256_DIGEST_SIZE],
                              &dummy_state.hash_state);
        /* Actual code for when key_size <= TC_SHA256_BLOCK_SIZE: */
        rekey(ctx->key, key, key_size);
    } else {
        (void)tc_sha256_init(&ctx->hash_state);
        (void)tc_sha256_update(&ctx->hash_state, key, key_size);
        (void)tc_sha256_final(&ctx->key[TC_SHA256_DIGEST_SIZE],
                              &ctx->hash_state);
        rekey(ctx->key,
              &ctx->key[TC_SHA256_DIGEST_SIZE],
              TC_SHA256_DIGEST_SIZE);
    }

    return TC_CRYPTO_SUCCESS;
}

int tc_hmac_init(TCHmacState_t ctx)
{
    /* input sanity check: */
    if (ctx == (TCHmacState_t) 0) {
        return TC_CRYPTO_FAIL;
    }

    (void) tc_sha256_init(&ctx->hash_state);
    (void) tc_sha256_update(&ctx->hash_state, ctx->key, TC_SHA256_BLOCK_SIZE);
    return TC_CRYPTO_SUCCESS;
}

int tc_hmac_update(TCHmacState_t ctx,
                   const void *data,
                   unsigned int data_length)
{
    /* input sanity check: */
    if (ctx == (TCHmacState_t) 0) {
        return TC_CRYPTO_FAIL;
    }

    (void)tc_sha256_update(&ctx->hash_state, data, data_length);
    return TC_CRYPTO_SUCCESS;
}

int tc_hmac_final(uint8_t *tag, unsigned int taglen, TCHmacState_t ctx)
{
    /* input sanity check: */
    if (tag == (uint8_t *) 0 ||
            taglen != TC_SHA256_DIGEST_SIZE ||
            ctx == (TCHmacState_t) 0) {
        return TC_CRYPTO_FAIL;
    }

    (void) tc_sha256_final(tag, &ctx->hash_state);
    (void)tc_sha256_init(&ctx->hash_state);
    (void)tc_sha256_update(&ctx->hash_state,
                           &ctx->key[TC_SHA256_BLOCK_SIZE],
                           TC_SHA256_BLOCK_SIZE);
    (void)tc_sha256_update(&ctx->hash_state, tag, TC_SHA256_DIGEST_SIZE);
    (void)tc_sha256_final(tag, &ctx->hash_state);
    /* destroy the current state */
    _set(ctx, 0, sizeof(*ctx));
    return TC_CRYPTO_SUCCESS;
}
